Method, device, base station and system for direct uplink access in a mobile communications network

ABSTRACT

The invention relates to a method between a communications device ( 110 ) and a communications network, which communications network generally provides at least a direct cell access mechanism and an alternative cell access mechanism for the communications device for uplink access to the communications network. The method comprises determining by the communications network and indicating ( 230 ) to the communications device ( 110 ) whether the direct cell access mechanism can at a given time be provided. This being the case, the communications device can directly start sending user data ( 150 ) on a traffic channel. In a situation in which the direct cell access cannot be provided, it is indicated to the communications device that the alternative cell access mechanism should be used.

FIELD OF THE INVENTION

The invention relates to uplink access in a communications system.

BACKGROUND OF THE INVENTION

One of the problems in the performance of current cellular mobilecommunications systems is the service access time, i.e. the duration ittakes after a user requests a service until the service is delivered.One important contributor to the lengthiness of the service access timeis the used cell access mechanism.

FIG. 1 shows the basic principle of a cell access mechanism widely usedin the second-generation cellular mobile communications systems. When aterminal 110 has user data to send it transmits to a network an accessrequest message 111 on a Random Access CHannel (RACH) and waits for aresponse from the network before user data can be transmitted. Forexample, in GSM GPRS (General Packet Radio Service), an access requestmessage is conveyed via a base station 120 to a base station controller(not shown) which may contain a unit performing radio resourceallocation. As a result, an access grant message 121 identifying adedicated radio transmission resource to be used for user datatransmission is transmitted from the network to the terminal 110 on anAccess Grant Channel (AGCH). After receipt of the access grant message121, depending on message contents, the terminal 110 either has to waitfor an assigned Uplink State Flag (USF) from the network before it canstart sending user data 150 or it can immediately start sending userdata 150 on the assigned Traffic Channel (TCH) as identified by theaccess grant message 121.

The cell access mechanism just described causes a relatively longminimum access delay before any user data can be transmitted. This isdue to the fact that radio resources must first be requested before userdata transmission can be started. The minimum access delay exists evenif the radio resources of the current base station are unoccupied.

Third generation cellular mobile communications systems presentimprovements to the situation. For example, in a WCDMA system (WidebandCode Division Multiple Access) user data can be transmitted in a RACHmessage but the amount of user data which call be included in a RACHmessage is very limited. Although a dedicated traffic channel (DCH)providing more radio resources may subsequently be set up, this is notan ideal solution e.g. for a terminal which would immediately desire tostart sending user data at a high data rate.

The WCDMA system also provides a Common Packet CHannel (CPCH) whichallows higher data rates but can not support mobility, such as normalhandovers or macrodiversity reception (i.e. soft handover).

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a methodbetween a communications device and a communications network, whichcommunications network generally provides at least a direct cell accessmechanism and an alternative cell access mechanism for thecommunications device for uplink access to the communications network,the method comprising:

determining by the communications network and indicating to thecommunications device whether the direct cell access mechanism can at agiven time be provided.

Preferably, said indicating comprises indicating whether thecommunications device can directly start sending user data on a trafficchannel.

In one embodiment, the determination whether the direct cell accessmechanism can be provided is made based on radio and/or trafficmeasurements performed by a base station.

Preferably, if the direct cell access cannot be provided, the methodcomprises indicating to the communications device that the alternativecell access mechanism should be used. In one embodiment, the alternativecell access mechanism comprises using a separate access channel, such asRACH, for uplink access.

In one embodiment, said indication is performed by including aparticular parameter value in a system information broadcast.

According to a second aspect of the invention, there is provided acommunications device configured for operation with a comminationsnetwork, which communications network generally provides at least adirect cell access mechanism and an alternative cell access mechanismfor the communications device for uplink access to the communicationsnetwork, the communications device comprising:

means for receiving an indication sent by the communications network,the indication indicating to the communications device whether thedirect cell access mechanism can at a given time be provided.

In one embodiment, the communications device is a mobile hand-helddevice of a cellular communications network.

According to a third aspect of the invention, there is provided a basestation of a communications network, which communications networkgenerally provides at least a direct cell access mechanism and analternative cell access mechanism for a communications device for uplinkaccess to the communications network, the base station comprising:

means for determining and indicating to the communications devicewhether the direct cell access mechanism can at a given time beprovided.

According to a for the aspect of the invention, there is provided asystem comprising a communications device and a communications network,which communications network generally provides at least a direct cellaccess mechanism and an alternative cell access mechanism for thecommunications device for uplink access to the communications network,the communications network comprising:

means for determining and indicating to the communications devicewhether the direct cell access mechanism can at a given time beprovided; and the communications device comprising:

means for receiving said indication.

Dependent claims contain preferable embodiments of the invention. Thesubject matter contained in dependent claims relating to a particularaspect of the invention is also applicable to other aspects of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described by way of examplewith reference to the accompanying drawing in which:

FIG. 1 shows a prior art cell access mechanism;

FIGS. 2 and 3 show all embodiment of the invention;

FIG. 4 shows a base station according to an embodiment of the invention;

FIG. 5 shows mobile terminal according to an embodiment of theinvention; and

FIG. 6 shows a layered protocol stack in an embodiment of the invention.

DETAILED DESCRIPTION

FIGS. 2 and 3 show an embodiment of the invention. In this embodiment, abase station 120 first determines and then signals to a terminal 110whether direct access to a traffic channel at a particular (high) datarate is permitted or whether an alternative cell access mechanism (witha lower initial data rate) should be used. In this embodiment, theterminal 110 is a mobile terminal and the base station 120 is a basestation of a cellular communications network which controls the accessto the network in a centralized manner. The mobile terminal 110 and thebase station 120 communicate with each other by means of radio frequencycommunication over an air-interface (radio interface).

The base station 120 continuously performs measurements concerning thecell it is serving. These measurements may involve both radio andtraffic measurements. Based on the measurements, the base station 120gets information on the congestion level of the cell. Based on thecongestion level, the base station 120 determines whether a directuplink access to a traffic channel at a high data rate can be enabled.The base station 120 informs the mobile terminal 110 of the availabilityof the direct uplink access. For this purpose, a suitable parameter isdefined. In this embodiment, this particular parameter is calledDirectCellAccess. The parameter has two possible values: Enabled andDisabled. The value Enabled may be indicated by a binary digit “1” andthe value Disabled may be indicated by a binary digit “0”.

The base station 120 broadcasts system information over the coveragearea of the cell it is serving. The broadcasting is effected by sendinga broadcast message which is received by terminals residing inside thecoverage area of the cell. In this embodiment, the parameter valueDirectCellAccess=Enabled or DirectCellAccess=Disabled is broadcasted asa part of the system information broadcast.

If the base station 120 determines that a direct uplink access to atraffic channel can be permitted (empty or lightly loaded cell), itperiodically sends the parameter value DirectCellAccess=Enabled as apart of the system information broadcast 230 (FIG. 2) of the cell. Thesystem information broadcast 230 is received by the mobile terminal 110.It reads an updated value of the DirectCellAccess parameter as often asinstructed by the parameter(s) in the system information broadcastregulating the update frequency of system information.

If the base station 120 determines that a direct uplink access to atraffic channel cannot be permitted (cell loaded with traffic), itperiodically broadcasts the parameter value DirectCellAccess=Disabled inthe system information broadcast message 340 (FIG. 3).

When direct uplink access is enabled and the mobile terminal 110 hasuser data to send, it can directly start sending user data 150 (FIG. 2)on a traffic channel after a synchronization procedure specified by aphysical layer (L1) (see FIG. 6 and the corresponding description) hasbeen completed. Information on the traffic channel to be used may becommunicated in an appropriate way to the mobile terminal 110. It may,for example, be communicated from the base station 120 beforehand. Also,if the system is a CDMA based system, the appropriate code(s) may becommunicated from the base station 120 to the mobile terminal 110beforehand. The term system is here considered to comprise a combinationof appropriate network elements (such as a base station) and terminals.

When direct uplink access is disabled and the mobile terminal 110 hasuser data to send, it shall not use direct uplink access but analternative cell access mechanism has to be used. In the embodimentshown in FIG. 3, the alternative method is the two-step cell accessmechanism already known as such from the prior art in which the mobileterminal 10 first sends an access request message 111 to the basestation 120 and waits for a access grant message 121 from the basestation 120 before starting to send user data 150 on a dedicated trafficchannel (DCH or similar) as identified by the access grant message 121.

Modifications to the embodiment of the invention just described andother embodiments will be described in the following.

It has been described that the base station 120 periodically sends theparameter value DirectCellAccess=Enabled/Disabled as a part of systeminformation broadcast 230, 340. In one alternative embodiment, theparameter value is sent, instead of a broadcast message, in a particularmulticast message which is sent to a limited set of mobile terminals.The set is formed of mobile terminals which in general, based on a usersubscription (or similar), have the right to use the direct uplinkaccess. In yet another embodiment, the parameter valueDirectCellAccess=Enabled/Disabled is sent as a point-to-point message toeach mobile terminal 110 having right to use the direct uplink access.In yet another embodiment, the applicability of the DirectCellAccessparameter to individual terminals is further regulated by anotherparameter in the system information broadcast. This other parameter candefine a certain pseudo-random group of terminals based on the leastsignificant bits of a unique identifier such as subscriber identifier,equipment identifier or similar.

In one embodiment, an expiration time is given by the system to theparameter DirectCellAccess. When e.g. the system information broadcastmessage is used, the expiration time may be specified as a constantvalue or as another parameter in the system broadcast message. If theparameter value DirectCellAccess=Enabled, but it has been expired, themobile terminal 110 may not use the expired parameter value, but has toretrieve a new one before it can start user data transmission accordingto the direct uplink access mechanism.

It has been described that the base station 120 performs measurementsconcerning the cell it is servings and that it determines based on thesemeasurements whether the direct uplink access can be enabled. Thesemeasurements may involve both radio and traffic measurements. Which ofthem is/are used depends on the implementation. Typical radiomeasurements which may be used are, for example, measurement of thereceived total wide band power, SIR (Signal to Interference Ratio)measurement, BER (Bit Error Rate) measurement, FER (Frame Error Rate)measurement or other measurement on radio signal quality. Especially,the received total wide band power indicates whether there are manyusers accessing to the uplink direction.

A reader has been given the idea that the base station 120 locallycontrols the use of radio resources in its cell coverage area by e.g.determining the state of the direct uplink access mechanism. However, itshould be clear that the final decision on the radio resources mayalternatively be performed by another network element. Decisions arepreferably performed by the base station 120, though, since this wouldreduce the delay experienced by the terminal 110.

A typical environment in which the use of the direct uplink access fitswell would be a packet switched system with small cell sizes and shortdata bursts (e.g. IP packet bursts (Internet Protocol)) and having onlylittle continuous traffic. In a lightly loaded cell, even if there ismore than one terminal sending data at a high data rate, collisions arenot very likely if the bursts are short. Thus, a high data ratetransmission with only a small access delay can be provided to arestricted amount of users without compromising system performance.

Another advantage is that close to all cell uplink capacity can, incertain situations, be used for transfer of user data. For example, if ahigh data rate user is the only user of the cell, RACH channel capacitymight either not be needed at all, or it needs to be reserved only for anew user to register to the cell or to perform handover to the cell.This kind of situation may arise e.g. with a private access point. Whendirect uplink access to a traffic channel is enabled, only a minimumamount of RACH channel capacity is needed since one user cannot collideand not many other users are expected to access via said access point.The “released” RACH channel capacity may thus be used for transfer ofuser data.

The basic ideas of the invention are, in principle, applicable to anydigital wireless or cellular system with centralized architecture. Thisincludes 2^(nd) and 3^(rd) generation and possible future generations ofcellular systems as well as wireless local area networks, where both lowdelay and high throughput efficiency are targeted. No restrictions areplaced on the general radio access method; it can be e.g. TDMA (timedivision multiple access) or CDMA (code division multiple access). Thesystem involved may be a multicarrier system, such as an OFDM(Orthogonal Frequency Division Multiplexing) based system as well.

FIG. 4 shows a base station 120 according to an embodiment of theinvention. The base station comprises a processing unit 420, a radiofrequency part 440 and a network interface 425. The processing unit 420controls the operation of the base station 120. The radio frequency part440 and the network interface 425 are coupled to the processing unit420. The radio frequency part 440 receives and transmits user data fromand to mobile terminals 110 which operate in the area of the cell whichthe base station 120 serves. Communication to and from the rest of thenetwork is performed via the network interface 425.

The processing unit 420 comprises a Radio Resource Control (RRC) block.The mentioned radio and traffic measurements are performed by the radiofrequency part 440 and/or the network interface 425 and analysed by theRRC block. The RRC block makes based on the analysis decisions onwhether direct cell access should be enabled or disabled and controlsthe radio frequency part 440 such that the right parameter value(DirectCellAccess=Enabled/Disabled) is sent at each time to mobileterminals 110 concerned.

In other words, what the base station 120 actually does is that itcontrols the use of radio resources in the cell by enabling anddisabling the usage of a cell access mechanism. Combining this methodwith other means known from cellular and wireless systems furtherimproves the efficiency of radio resource usage. When the cell is emptyor lightly loaded, the base station 120 enables direct sending of userdata on high data rate with only a small access delay. When thecongestion level in the cell increases, only a slower access mechanismis permitted to be used in order to avoid collisions on the high datarate channel thereby saving radio resources.

FIG. 5 shows a mobile terminal 110 according to an embodiment of theinvention. In this embodiment, the mobile terminal 110 is a cellularmobile terminal comprising a processing unit MCU, a radio block 540 anda user interface UI. The processing unit MCU controls the operation ofthe mobile terminal 110 with the aid of software SW. The software SWresides in a memory 515. The radio block 540 and the user interface UIare coupled to the processing unit 420. The radio block 540 receives andtransmits user data from and to the base station 120 by means of radiocommunication over an air-interface. The user interface UT may comprisea keyboard, a display, a microphone and a speaker (not shown) forenabling the user of the mobile terminal 110 to use the terminal 110.

The system information broadcast (or another message) 230, 340 carryingthe parameter value DirectCellAccess=Enabled/Disabled is received viathe radio block 540 and processed by the processing unit MCU. Thesoftware comprises a protocol layer corresponding to the RRC layer ofthe base station 120. Said protocol layer interprets the receivedparameter value and controls the radio block 540 so that the rightaccess mechanism (direct cell access or an alternative mechanism) isused.

FIG. 6 shows how the air-interface (radio interface) between the mobileterminal 110 and the base station 120 (or network) is layered intoprotocol layers according to the WCDMA system. A protocol stack havingthree layers is formed. Each protocol layer implemented in the mobileterminal 110 communicates with a corresponding protocol layerimplemented in the base station 120 (or network).

The lowest layer is the physical layer (Layer 1 (=L1)). The physicallayer provides transport services to higher layers of the protocolstack. It provides transport channels for communication, such as theRACH, CPCH and DCH mentioned in the foregoing description.

The second lowest layer (L2) is the radio link layer. It provides datatransfer on logical channels. The logical channels can be divided intocontrol and traffic channels, wherein the control channels are used fortransfer of control information only and the traffic channels are usedfor transfer of user data. Both types of channels are mapped onto the L1transport channels.

The layer (L3) above the radio link layer is called the network layer.One of its functions in a radio system is radio resource control whichis performed by an RRC sublayer.

In one embodiment of the invention, the information on the availabilityof the direct access mechanism (DirectCellAccess parameter value) istransmitted on the network level (L3). The RRC sublayer is capable ofmobility services, such as handovers. Therefore, after high-speed userdata transmission has begun in accordance with the direct uplink accessmechanism on a traffic channel, the transmission can be continued duringa possible handover. This is not possible e.g. with the prior art CPCHmethod in which transmission has to be stopped if transmissionconditions weaken.

The traffic channel on which the mobile terminal 110 can directly startsending user data according to the direct uplink access mechanism, maybe defined as a channel on which all the necessary RRC functions can beimplemented, i.e. in this case a traffic channel of the radio link layer(L2).

The layers L1, L2 and L3 can be implemented by a suitable combination ofhardware and software in the mobile terminal 110 (FIG. 5) and basestation 120 (FIG. 4).

Particular implementations and embodiments of the invention have beendescribed. It is clear to a person skilled in the art that the inventionis not restricted to details of the embodiments presented above (e.g.the parameter names, the configuration of the protocol layers), but thatit can be implemented in other embodiments using equivalent meanswithout deviating from the characteristics of the invention. The scopeof the invention is only restricted by the attached patent claims.

1. A method for a system comprising a communications device and acommunications network, the method comprising: allocating, by thecommunications network, at least a direct cell access channel for thecommunications device for uplink access to the communications network,the direct cell access channel to permit the communications device todirectly start sending user data on the direct cell access channelwithout requesting access resources when user data is available to send;providing an alternative uplink transmission mechanism for thecommunication device to send data to the communications network if thedirect cell access channel cannot be provided; determining by thecommunications network conditions when the direct cell access channel isavailable for use at a given time; providing the communications devicewith a periodic availability message indication of the availability foruse of the direct cell access channel during said conditions; andpermitting reception of a transmission from the communications devicewithout a channel request during said availability.
 2. A methodaccording to claim 1, wherein in a situation in which the direct cellaccess can not be provided the method comprises: indicating to thecommunications device that the alternative cell access mechanism shouldbe used.
 3. A method according to claim 2, wherein the alternative cellaccess mechanism comprises using a separate access channel for uplinkaccess.
 4. A method according to claim 1, wherein a radio interfacebetween the mobile communications device and the communication networkis layered into protocol layers which form a protocol stack, and thedirect cell access channel forms part of a logical traffic channeloperating on a data link layer (Layer 2) of the protocol stack.
 5. Amethod according to claim 4, wherein said providing a periodicavailability message is carried out on a network layer (Layer 3) of theprotocol stack.
 6. A method according to claim 1, wherein said providinga periodic availability message is performed by sending a broadcastmessage to a set of communications devices including said communicationsdevice.
 7. A method according to claim 6, wherein said broadcast messagecontains a parameter value further restricting the set of communicationsdevices.
 8. A method according to claim 1, wherein said providing aperiodic availability message is performed by sending a multicastmessage to a limited set of communications devices including saidcommunications device.
 9. A method according to claim 1, wherein saidproviding a periodic availability message is performed by sending apoint-to-point message to the communications device.
 10. A methodaccording to claim 6, wherein said message conveys to saidcommunications device a parameter value indicating whether the directcell access channel is enabled.
 11. A method according to claim 1,wherein the communications network comprises a base station serving acell of a mobile communications system, and wherein the methodcomprises: performing one or more traffic and/or radio measurements bythe base station; and determining by the base station whether the directcell access channel can, at a given time, be provided to thecommunications device, on the basis of said measurements.
 12. A basestation of a communications network, comprising: means for allocating atleast a direct cell access channel to a communications device, thedirect cell access channel to enable the communications device todirectly start transmitting data on the direct cell access channelwithout first requesting access resources when the communications devicehas data to be sent; means for providing an alternative cell accessmechanism for the communications device for uplink access to thecommunications network if the direct cell access channel cannot beprovided; means for determining by the communications network conditionswhen the direct cell access channel is available for use at a giventime; means for providing the communications device with a periodicbroadcast message indication of the availability for use of the directcell access channel during said conditions; and means for permittingreception of a transmission from the communications device without achannel request during said availability.
 13. A system comprising acommunications device and a communications network, the communicationsnetwork comprising: means for allocating at least a direct cell accesschannel to a communications device, the direct cell access channel toenable the communications device to directly start transmitting data onthe direct cell access channel without first requesting access resourceswhen the communications device has data to be sent; means for providingan alternative cell access mechanism for the communications device foruplink access to the communications network if the direct cell accesschannel cannot be provided; means for determining by the communicationsnetwork conditions when the direct cell access channel is available foruse at a given time; means for providing the communications device witha periodic broadcast indication of the availability for use of thedirect cell access channel during said conditions; and means forpermitting reception of a transmission from the communications devicewithout a channel request during said availability; and thecommunications device comprising: means for receiving said indication.14. An apparatus, comprising: a module to allocate to a communicationsdevice at least a direct cell access channel to permit thecommunications device to directly start sending uplink data to acommunications network on the direct cell access channel withoutrequesting access resources when uplink data is available to send; amodule to provide to the communications device an alternative cellaccess mechanism for uplink access to the communications network whenthe direct cell access channel cannot be provided; and a determinationmodule to determine conditions when, at a given time, the direct cellaccess channel can be provided; and a transmitter to provide to thecommunications device a periodic broadcast message indication of theavailability of the direct cell access channel during said conditions;and a receiver to receive a transmission from the communications devicewithout a channel request during said availability.
 15. An apparatusaccording to claim 14, wherein the apparatus is configured to operate asa base station of the communications network.
 16. An apparatus accordingto claim 14, wherein, in a situation in which the direct cell accesschannel can not be provided, the apparatus is configured to indicate tothe communications device that the alternate cell access mechanismshould be used.
 17. An apparatus according to claim 14, wherein thealternative cell access mechanism comprises using a separate accesschannel for uplink access.
 18. An apparatus according to claim 14,wherein said availability message comprises an indication of whether thecommunications device can directly start sending user data on the directcell access channel at a high data rate.
 19. An apparatus according toclaim 14, wherein a radio interface between the apparatus and thecommunications device is layered into protocol layers which form aprotocol stack, and the direct cell access channel forms part of alogical traffic channel operating on a data link layer (Layer 2) of theprotocol stack.
 20. An apparatus according to claim 19, wherein saidtransmitter is to provide the periodic availability message using anetwork layer (Layer 3) of the protocol stack.
 21. An apparatusaccording to claim 14, wherein the availability message comprises abroadcast message, a multicast message, or point-to-point message(s).22. An apparatus according to claim 14, wherein the availability messagecomprises a broadcast message, and wherein said broadcast messagecontains a parameter value restricting a set of communications devicesto which the message is to be transmitted.
 23. An apparatus according toclaim 14, wherein the availability message comprises a messagecomprising a parameter value indicating whether the direct cell accesschannel is enabled.
 24. An apparatus according to claim 14, wherein theapparatus is configured to operate as a base station of thecommunications network, and wherein the determination module is toperform traffic and/or radio measurements and to determine whether thedirect cell access can, at a given time, be provided on the basis ofsaid measurements.
 25. A method according to claim 1, wherein, in thealternative cell access mechanism, a two step process occurs in whichthe communications device first requests access to the communicationsnetwork.